1. Field of the Invention
This invention relates to the transportation of a granular substance such as sand and, more particularly, to the modification of cargo containers for the purpose of transporting sand therein to frac sites.
2. Description of the Prior Art
Cargo containers (also called intermodal containers, freight containers, ISO containers, shipping containers, Hi-Cube containers, Sea Cans) are standardized, reusable steel boxes used for the safe, efficient and secure storage and movement of materials and products within a global containerized freight transportation system. The container can be moved from one mode of transportation to another without unloading and reloading the contents of the container. All of the containers are 8 ft. wide so they can travel along standard highway systems. The height of the standard container is normally 8 ft. 6 in., but a “high cube” container of 9 ft. 6 in. in height can be used.
The part of the standard cargo container that may change is the length. The standard length size is either 20 ft. or 40 ft.
A general purpose cargo container has doors fitted at one end and is constructed of corrugated weathering steel. The cargo containers can be stacked up to seven containers high. At each of the eight corners are castings with openings for twist-lock fasteners to hold the cargo containers in position. It is estimated there are 17 million cargo containers available world-wide.
In the last two years, hydraulic fracturing (also known as “fracing”) has been used in hydrocarbon wells to create cracks in underground reservoir rock formations to create new channels in the rock, which increases the extraction rate and ultimate recovery of fossil fuels. To keep the fractures from closing, during the fracing process, a proppant is injected with a fluid, which proppant keeps the fractures open once the pressure is released. The most common proppant used is sand, although in recent years other proppants such as resin-coated or ceramic sand have been utilized.
In reservoirs such as shale rock or coal beds, fracing may be used to cause the production of natural gas or oil from those formations. Otherwise, there is not sufficient viscosity, permeability or reservoir pressure to allow the natural gas or oil to flow from the rock into the well bore at economic rates. Fracturing will provide flow paths connecting a larger area of the reservoir to the well, thereby increasing the area from which natural gas or liquids can be recovered from a formation. In such case, a proppant, such as sand, is necessary to keep the fractures open with the oil and gas flowing there through.
In the fracturing of a single well, the amount of proppant such as sand that is used can cost five or six million dollars. Most of the cost of the sand is for handling. If the sand can be handled fewer times, the cost can be greatly reduced.
The type of sand used in fracing is also very critical. The sand should have high quartz content so that it will not crush in the cracks of the formation, but will hold the cracks open. The deeper the well, normally the more quartz content that is required. In order to get the appropriate types of sand, fracing companies are having to purchase it throughout the world. For example, in deep wells in South Texas, the good quality fracing sand comes from such places as the State of Wisconsin, China, or Russia. From other countries, the sand is delivered to the United States by ship and is handled at multiple locations in multiple ways with very inefficient supply chain logistics for the handling of the fracing sand. The more times the fracing sand is handled, the more expensive it is to the individual fracing company and to the well operator. This is passed along to the consumer in the increased price of gasoline.
Also at the well site if a truck delivers sand and cannot unload when the truck arrives, then the operator is charged the demurrage for waiting. It is common at many frac sites for a number of trucks to be waiting in line to be unloaded, for which the operator is being charged demurrage. It is important that as soon as the sand is delivered to the frac site, that it can be immediately unloaded to eliminate the demurrage.